The field of this invention relates to an improved spark plug for an internal combustion engine and more particularly to a spark plug which produces a substantially increased operating efficiency of the internal combustion engine.
Spark plugs are used in most internal combustion engines (except diesel engines) to provide high voltage sparks which ignite the fuel/air mixture within the combustion chambers of the engine. When the engine is running, a pulse of electrical energy, at very high voltage, is delivered to the terminal of the spark plug at the correct moment by means of a distributor. A spark is caused to jump the gap between the center electrode an the ground electrode, the latter being earthed to the cylinder block of the engine. This spark provides the energy needed to ignite the compressed fuel/air mixture in the cylinder of the engine.
It has been found that, for optimum performance, the temperature of the core nose at the firing end of a spark plug should not drop below four hundred degrees centigrade nor exceed about eight hundred fifty degrees centigrade. Below four hundred degrees centigrade, deposits of carbon and oil are likely to accumulate. Carbon being electrically conductive, can provide a short circuit path for the high voltage pulse and so weaken or eliminate the spark. Core nose temperatures of above eight hundred degrees centigrade can cause excessive electrode erosion and possibly uncontrolled ignition of the fuel/air mixture in advance of the timed spark. This condition (called pre-ignition) can cause serious engine damage.
In recent years there has been an enormous increase in the use of spark plugs on which the core nose projects beyond the end of the threaded body. Generally, the extra-long core nose runs hotter than other types of spark plugs at low engine speeds giving improved protection against plug fouling. At high engine speeds, the exposed core nose is cooled by the incoming fuel/air mixture, thus avoiding the risk of plug overheating.
The conventional type of spark plug utilizes a strip-type of ground electrode which overlies the tip of the center electrode. This strip assumes a slight gap from the center electrode across which the spark is to occur. This type of spark plug has but one spark presentation, that being that the spark occurs at approximately the same location each time the spark plug is operated. Any accumulations of oil or carbon, not located directly in the path of the firing of the spark plug, will remain adhered to the surface of the spark plug and will accumulate and result in inefficient usage of the spark plug.
Spark plug bodies are generally made of high quality steel and are zinc plated to avoid corrosion. The insulators, which surround the center electrode, are made from a fired aluminum oxide ceramic material which is highly resistant to thermo and mechanical stress and chemical attack. The center electrodes are most commonly made from nickel alloys, but precious metals sometimes are used. Gas tight seals are required between the center electrode and insulator and also between the insulator and housing. These seals are normally formed from aluminum oxide powder (termed sillment) which when compressed becomes a rigid mass which fits the available space exactly.
In this day and age in which exhaust emissions are closely controlled, there is a need to construct a spark plug which causes the fuel/air mixture of the engine to burn more completely and evenly thereby decreasing the amount of pollutants created during combustion.